The invention relates to fluid mixing devices and particularly to devices suitable for mixing a liquid detergent with a stream of water.
In particular the invention relates to a fluid mixing device of the kind comprising a body part having an inlet for connection to a source of a first fluid, such as water, under pressure, a main flow passage leading from said inlet to an outlet from the body part, means within the main flow passage for creating a low pressure zone in that passage during flow of the first fluid therethrough, and an auxiliary passage leading to said low pressure zone and for connection to a source of a second fluid, such as liquid detergent. In such a device, the creation of the low pressure zone due to the flow of the first fluid causes the second fluid to be drawn into the main flow passage and to be entrained with the first fluid so that the two fluids emerge together from the outlet of the device.
In a device of this kind it is desirable to be able to cut off the supply of the second fluid when required. Hitherto, this has been achieved by providing a valve controlled vent leading to the main flow passage, by means of which vent the low pressure zone may be placed in communication with the ambient atmosphere. Since, when the vent is opened, ambient air is more easily drawn into the low pressure zone than is the second fluid, the flow of the second fluid will cease. Such an arrangement has the disadvantage that the provision of the air vent, and its associated control valve, is costly, and the device is also liable to malfunction due to leakage in the air valve assembly. The invention sets out to provide a fluid mixing device which avoids these drawbacks.